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Area forecast discussion
National Weather Service Buffalo New York
1016 PM EDT Wed Sep 18 2019

an area of strong high pressure will provide US with a prolonged
stretch of magnificent late Summer weather for the rest of the week,
with temperatures climbing to well above normal by late in the week.
The next chance of rain will not arrive until Sunday night.


Near term /through Thursday night/...
a 1028mb high will remain in place over eastern Quebec and northern
New England tonight, with a ridge extending down into the eastern
Great Lakes. This will provide clear skies through the late evening
hours with nothing more than some thin/high cirrus.

A building mid-level ridge will track overhead tonight and while
little change will occur at the surface, warmer temperatures will
begin to filter into the region aloft. Clear skies and dry air will
result in another night of strong radiational cooling. River Valley
fog is likely again across the southern tier. Low temperatures will
again drop to the upper 40s to lower 50s on the lake plains, with
low to mid 40s across the interior southern tier valleys. East of
Lake Ontario, lows will be in the upper 30s to lower 40s, with a few
spotty mid 30s readings and patchy light frost in Lewis County.
Similar to the past few nights, coverage of frost is not expected to
be great enough to justify a frost advisory.

On Thursday, high pressure will continue to drift slowly east across
New England, with associated subsidence and dry air dominating our
region. After valley fog dissipates, the warmer temperatures aloft
and sunshine will result in temperatures reaching the low to mid
70's Thursday afternoon, with a few upper 70s possible across the
Niagara Frontier.

Thursday night low temperatures will be a few degrees warmer than
previous nights as low level warm advection slowly increases around
the western periphery of the departing High. River valley fog is
likely again across the southern tier.


Short term /Friday through Sunday night/...
well advertised upper ridge from the south central Continental U.S. Toward
Hudson Bay expands across the Great Lakes and into the northeast
Continental U.S. By this weekend. Sfc high pressure from Atlantic Canada to the
lower Great Lakes reorients by Friday, with high pressure center
settling along the East Coast with secondary ridge from Hudson Bay
to the lower Great Lakes. Overall this pattern brings warmer air
aloft into New York by the weekend with 850 mb temps rising to 13-15c by
Saturday and into the mid teens by Sunday. Initially as the high
pressure ridge is close by, forecast soundings indicate we will not
tap into these very warm temps aloft due to subsidence inversion
around 900mb/3kft above ground level. However, later Saturday afternoon and into
Sunday, mixing increases where high temps should reach into at least
the lower if not mid 80s in some locations.

Main question on Sunday is how quick will a pre-frontal trough ahead
of main cold front, and the associated showers, arrive from the
west? GFS remains quickest as edge of stronger moisture transport
and entrance region of upper jet would support some showers into
western New York mid to late afternoon. European model (ecmwf) shows similar features
driving the showers, but is overall 6-12 hours slower. Canadian
is a compromise solution. Forecast soundings indicate mid clouds
invading as early as Sunday morning, but more significant deeper
moisture with precipitable waters over 1.75 inches not arriving until Sunday
evening. Prefer to lean toward slower ideas since the pre-frontal
trough and main cold front will be parallel to the upper flow and
since the mid-level winds through Sunday are SW instead of W which
would drive showers into western New York. For now, brought low-end
chances to western New York after 21z, ramping up to likely pops across
the board by later Sunday evening as axis of deep moisture arrives.
After a warm start for temps on Sunday morning, kept highs into the
lower 80s western New York toward mid 80s southeast of Lake Ontario and
toward Finger Lakes. If cloud cover is thicker, then highs could be
held back into the upper 70s to lower 80s from west to east.

Looks like there will be a couple periods of showers work through
Sunday night on into Monday. All models trending toward better
chance for rainfall all areas on Monday with stronger shortwave
working through in overall troughing aloft. Went for likely pops all
areas on Monday. Though guidance doesn't explicitly show it, could
be some thunder especially western New York as edge of plume of elevated
instability tries to advect in. Probably just a few rumbles and
certainly not enough of a signal to put in the forecast attm.
Lastly, as previous shift mentioned, remnant deeper moisture from
what once was briefly ts Imelda may be around on Monday as the main
front moves through which would only help enhance heavy rain
chances. Even without that though, given precipitable waters above 1.5 inches, may
see some heavy rain at times later Sunday night through Monday.
Though with the rain and cloud cover it will be cooler compared to
the Friday - Sunday time frame, readings on Monday even in the lower
to middle 70s will be above normal as normal highs are in the upper
60s to near 70f.

No choice but to hang on to at least lower chance pops through much
of Monday night due to slower trend in exiting the system. Best
chances for showers, especially overnight, should remain south and
east of our area.


Long term /Monday through Wednesday/...
gradual improvement Tuesday into Wednesday in the wake of mid level
shortwave trough moving offshore over the Atlantic. 850 mb temps by
Tuesday afternoon will be in the vcnty of 6c, so it will certainly
be cooler. Afternoon highs Tuesday should be in the upper 60s to
near 70, which will still be a couple ticks above normal. Dry
weather extends into Wednesday with temperatures reaching back into
the lower to middle 70s.


Aviation /02z Thursday through Monday/...
high pressure will continue to drift slowly east across New England
tonight and Thursday, with associated dry air and subsidence
providing VFR for most areas with nothing more than some thin/high
cirrus at times. The one exception will be across the western
southern tier, where River Valley fog will form again from about 06z-
14z Thursday with local IFR. This is not expected to impact kjhw.

Friday through Sunday...mainly VFR...with localized IFR
in southern tier valley fog possible each night/early morning.
Sunday night and Monday...areas of MVFR with showers likely.


high pressure will provide our region with light winds and minimal
wave action for the rest of the week. There will be a few periods of
modestly higher east-northeast winds in the 10-13 knot range that will boost
waves to around 2 feet briefly. This will occur this evening on Lake
Erie and Western Lake Ontario, and again Thursday afternoon and
evening in the same locations as lake breezes mature.


Buf watches/warnings/advisories...
New York...none.



near term...Hitchcock/hsk

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